Apparatus for driving electrical loads provided at a car

ABSTRACT

A power supply system for a car in which a first group of loads is selected by a key switch and fed power via a fuse, while a second parallel connected group of loads is fed power without a fuse via respective ones of control units coupled to transmission lines for controlling each of the second group of loads.

This application is a continuation of application Ser. No. 08/954,893,filed Oct. 21, 1997, now U.S. Pat. No. 5,825,097, which is acontinuation of 08/698,107, filed Aug. 15, 1996, now U.S. Pat. No.5,710,465.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to an apparatus for driving a plurality ofelectrical loads of a vehicle by feeding electricity to the loads from asingle power source.

An apparatus for driving electrical loads of a car, for example, isdisclosed in JP-A-77680/1993.

The disclosed apparatus estimates a permissible supply power of abattery and a total consumption power of electrical loads, and regulatesthe power fed to loads of a lower functional priority, such as a reardefogger, a sheet heater, and so forth.

Even if the above-mentioned apparatus is used, a large current, referredto as a rush current, is needed on starting an electrical load.Therefore, nevertheless the fed power for loads of a lower functionalpriority is stopped, engine speed decreases in response to thegenerator's increasing its generated power output, and the load on theengine rapidly increases, on starting of the electrical loads. That is,the existing apparatus causes the engine speed to rapidly change whenthe electrical loads are started.

The present invention has been achieved in consideration of theabove-described problem, and is aimed at providing an apparatus fordriving electrical loads of a car, in which the engine speed does notrapidly change, even if operational states of an electrical load change.

To attain the above-mentioned objective, the present invention providesan apparatus for driving electrical loads of a car, comprising:

a plurality of direction devices comprising load switches, each of thedirection devices being provided at one of a plurality of electricalloads arranged at the car, for directing an ON/OFF state of the one ofthe plurality of electrical loads;

storage apparatus or a memory for storing an increase rate per unit timeof power feeding (hereafter referred to a power feeding increase rate)preset for each of the plurality of electrical loads when acorresponding one of the direction devices indicates a state transitionfrom an OFF state to an ON state;

a plurality of drive devices comprising an output front stage transistorand an output driving stage transistor, each of the drive devices beingprovided at each of the plurality of electrical loads, for feeding powerto the one of the plurality of electrical loads and for changing theamount of a power fed to the one from a power source; and

control apparatus comprising a CPU for checking an operational state ofeach of the plurality of electrical loads, and, if the control apparatushas judged that at least one of the direction devices has indicated thestate transition, sending such a control signal to a corresponding oneof the drive devices that power is fed to a corresponding one of theelectrical loads from the power source, with a power feeding increaserate preset and stored in the storage-apparatus, corresponding to theelectrical load.

In the above-mentioned apparatus for driving the electrical loads,further, the storage apparatus stores a minimum ratio of power feeding(hereafter referred to a minimum power feeding ration) preset for eachof the plurality of the electrical loads, which is kept even at a OFFstate of a corresponding one of the direction devices, and the controlapparatus sends such a control signal to a corresponding one of thedrive devices that power is fed to a corresponding one of the electricalloads from the power source, which is at a stopping state, with aminimum power feeding ratio preset and stored in the storage apparatus,corresponding to the electrical load at the stopping state.

In the above-mentioned apparatus for driving the electrical load,further, an engine state detector comprising a key switch, anaccelerator opening sensor and an engine revolution speed sensor fordetecting an operational state of an engine of the car is included. Thestorage apparatus stores a power feeding increase rate preset for eachof the plurality of electrical loads, according to each of thepredetermined operational states of the engine, and the controlapparatus or CPU checks a switching state of each of the plurality ofdirection devices. If the control apparatus judges that at least one ofthe direction devices has indicated the state transition, it sends sucha control signal to a corresponding one of the drive devices that poweris fed to a corresponding one of the electrical loads from the powersource, with a power feeding increase rate preset and stored in thememory, corresponding to the electrical load and according to anoperational state of the engine detected by the engine state detector.

In the above-mentioned apparatus for driving the electrical loads, theengine state detector includes an engine starting state detector fordetecting whether the engine is at a starting state, the storageapparatus stores data indicating whether power is to be fed to each ofthe plurality of electrical loads, depending on functional importance ofa corresponding one of the electrical loads, when a corresponding one ofthe direction devices directs driving of the corresponding one of theelectrical loads at the starting state of the engine, and the controlapparatus determines whether power is to fed to one of the plurality ofelectrical loads, of which driving is directed by one of the directiondevices, and sends such a control signal to a corresponding one of thedrive devices that power feeding to the corresponding one of theelectrical loads is stopped if the control apparatus determines it isnot necessary to feed power to the electrical load. Power feeding to thecorresponding one of the electrical loads is continued if the controlapparatus determines it is necessary to feed power to the electricalload, by referring to the data stored in the memory.

In the above-mentioned apparatus for driving the electrical loads,further, the engine state detector includes an accelerator operatingamount detector for detecting an operation amount of an acceleratorpedal operated by an operator, the storage apparatus stores a decreaserate per unit time of power feeding (hereafter referred to a powerfeeding decrease rate) preset for each of the plurality of electricalloads if an acceleration required by an operator exceeds thepredetermined value, and the control apparatus estimates theacceleration required by an operator based on the operation amount ofthe accelerator pedal detected by the accelerator operating amountdetector, and sends such a control signal to a corresponding one of thedrive devices that power is fed to one of the plurality of electricalloads, of which driving is directed by one of the direction devices,with a power feeding decrease rate preset and stored in the storageapparatus, corresponding to the electrical load.

In the above-mentioned apparatus for driving the electrical loads, afuel amount detector is provided for detecting a residual fuel amountleft in a fuel tank of the car, the storage apparatus stores a decreaserate per unit time of power feeding (hereafter referred to a powerfeeding decrease rate) preset for each of the plurality of electricalloads, the power feeding decrease rate for each of the plurality ofelectrical loads being used when the residual fuel amount is less thanthe predetermined value, and the control apparatus sends such a controlsignal to a corresponding one of the drive devices that power is fed toone of the plurality of electrical loads, of which driving is directedby one of the direction devices, with a power feeding decrease ratepreset and stored in the memory, corresponding to the electrical load,if the residual fuel amount detected by the fuel amount detector is lessthan the predetermined value.

As mentioned above, if at least one of the direction devices indicatesthe state transition from a stopping state to an operation state, thecontrol apparatus sends such a control signal to a corresponding one ofthe drive devices that power is fed to a corresponding one of theelectrical loads with a power feeding increasing rate preset and storedin the memory, corresponding to the electrical load. Thus, power is fedto the electrical load with the preset power feeding increase rate fromthe power source. That is, when starting of an electrical load isdirected by one of the direction devices manipulated by an operator,power feeding to the electrical load starts and the ratio of the powerfeeding gradually increases. Therefore, at the stating state of anelectrical load, because it hardly happens that the generator rapidlyincreases the generated power, and puts a rapid load on the engine, theengine speed can be kept stable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus for driving electrical loadsof an embodiment in the present invention.

FIG. 2 is a block diagram showing a circuit of a control unit of theembodiment.

FIG. 3 is a diagram showing examples of changing rates of power feeding,KR and KF, and the minimum power feeding ratio Dmin of the embodiment.

FIG. 4 is a composite of three graphs showing changes of a load drivingvoltage and a duty ratio for a corresponding electrical load inaccordance with changes of a directing state of a load switch, in theembodiment.

FIG. 5 is a graph showing changes of a duty ratio during a transientstate started by a state transition operation from an OFF state to an ONstate of a load switch, in the embodiment.

FIG. 6 is a part No.1 of a flow chart showing operations of the controlunit of the embodiment.

FIG. 7 is a part No.2 of a flow chart showing operations of the controlunit of the embodiment.

FIG. 8 is a part No.3 of a flow chart showing operations of the controlunit of the embodiment.

FIG. 9 is a part No.4 of a flow chart showing operations of the controlunit of the embodiment.

FIG. 10 is a schematic diagram of an apparatus for driving electricalloads of a vehicle in accordance with the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an apparatus for driving electrical loads in a vehicle, ofthe present invention, will be explained in detail by referring to thedrawings.

As shown in FIG. 1, the apparatus for driving electrical loads providedin a car is composed of a battery 1, a key switch 2 for starting anengine, an AC generator 3 rotated or powered by the engine, electricalloads such as lamps 5, motors 6 and so forth, load switches 4 fordirecting start/stop of the electrical loads 5, 6, etc., an acceleratoropening sensor 8a for detecting an operation amount of an acceleratorpedal, a fuel amount sensor 8b for detecting a residual fuel amount leftin a fuel tank of the car, an engine revolution speed sensor 8c fordetecting the number of engine revolutions, and a control unit 10 forcontrolling power fed to each of the electrical loads 5, 6, etc. from apower source.

The power is fed to the control unit 10 via a fuse 9 from a positiveelectrode of the battery 1. To the control unit 10, each of states ofthe key switch 2 (ACC: operation of accessories, IGN: operation ofignition and STT: operation of a starter) is input to determine anoperational state of the engine. The control unit 10 also takes insignals from the fuel amount sensor 8b and the engine revolution speedsensor 8c. Further, the control unit 10 monitors a ON/OFF state of theload switches 4, and controls the electrical loads 5, 6, etc. and the ACgenerator 3, in accordance with procedures prepared in advance,according to outputs from the key switch 2 and the sensors 8a, 8b and8c.

As shown in FIG. 2, the control unit 10 is composed of a microcomputer11 for controlling the electrical loads and other electrical equipment,a regulator 12 for keeping the voltage of the battery 1 at a targetconstant value (5V), an input stage transistor 19a for inputting a ONsignal of the ACC to the microcomputer 11 when the key switch is turnedto a position of the accessories (ACC), an input stage transistor 19bfor inputting a ON signal of the IGN to the microcomputer 11 when thekey switch is turned to a position of the ignition (IGN), an input stagetransistor 19c for inputting a ON signal of the STT to the microcomputer11 when the key switch is turned to a position of the starter (STT), andinput stage transistors 13, one of the transistors 13 for inputting a ONsignal of the one of the load switches 4 to the microcomputer 11 whenone of the load switches 4 is turned on. Further, the control unit 10 iscomposed of an output driving stage transistor 15 for driving theelectrical load 5 by feeding power to the load 5 from the battery 1, anoutput front stage transistor 14 for driving the output drivingtransistor 15 in accordance with a drive signal from the microcomputer11, an output driving stage transistor 17 for feeding power to a fieldcoil 3a of the AC generator 3 from the battery 1, an output front stagetransistor 16 for driving the output driving transistor 17 in accordancewith a drive signal from the microcomputer 11, and signal processingcircuits 18a, 18b and 18c for converting signal levels of outputs fromthe sensors 8a, 8b and 8c to the levels at which the microcomputer 11can process the signals. The microcomputer 11 is composed of a memory11b storing various kinds of data and programs for realizing flow chartsshown in FIGS. 6-9 by using a table containing control parameters shownin FIG. 3, and a CPU 11a for executing calculations instructed by theprograms stored in the memory 11b. Further, the AC generator 3 iscomposed of a stator coil 3c of a stator, the field coil 3a of a part ofa rotor, and a brush 3b for feeding power to the rotating field coil 3afrom the battery 1. In the AC generator 3, when the current flows in thefield coil 3a of the rotor rotated by the engine, the field coil 3a isexcited, and the current flows in the stator coil 3c, that is, the ACcurrent is generated. Meanwhile, although only one load switch andone-electrical load are indicated in FIG. 2 to simplify the figure,there are actually a plurality of load switches and electrical loads asshown in FIG. 1.

The voltage of the battery 1 is decreased to the optimal voltage (5V)for the control microcomputer 11 by the regulator 12, and fed to themicrocomputer 11. The input stage transistor 13 is turned on/off inaccordance with an on/off state of the load switch 4, and converts thelevel of the state signal of the load switch 4 so that the microcomputer12 can takes in the state signal of the load switch 4. The output frontstage transistor 14 is used to drive the output drive stage transistor15, corresponding to a drive signal output from the microcomputer 11 viaa digital signal output port DO. The output drive stage transistor 15 isturned on/off in accordance with an on/off state of the output frontstage transistor 14, and drives the electrical load 5 by feeding powerto the electrical load 5 from the battery 1. For controlling of theelectrical load 5, the PWM (Pulse Width Modulation) method is applied. Aterminal voltage of the electrical load 5 is fed back to themicrocomputer 11 via an A/D converting input port. The microcomputer 11has a function of regulating the power generated by the AC generator 3based on a difference between the standard voltage of the battery andthe battery voltage level-converted by a resistive divider which isconverted to a digital signal by an A/D port. The power generated by theAC generator 3 is controlled by adjusting the current flowing in thefield coil 3a of the AC generator 3 with the output drive stagetransistor 17 derived by a field current control signal output from themicrocomputer 11 via a digital signal output port DO. The levels ofoutputs from the sensors 8a and 8b are converted to levels adequate toprocessing of the microcomputer 11 by the signal processing circuits 18aand 18b, and the processed outputs are taken into A/D converting portsof the microcomputer 11. By the signal processing circuit 18c, waveformshaping of the output from the engine revolution speed sensor 18c iscarried out and the level of the output is converted to a level adequateto processing of the microcomputer 11. The processed output is input toa digital signal input port DI. These sensor signals can be taken in byusing a transmitting port if the signals are processed as mentionedabove, by using a separate signal processing circuit.

Meanwhile, the above-mentioned PWM control method is explained asfollows, by referring to FIG. 4.

In the embodiment, the output drive stage transistor 15 controls theduty ratio of the current flowing in the electrical load by repeatingon/off operations so as to flow intermittent current in the electricalload and to adjust the on-state time ratio of the output drive stagetransistor 15. The above-mentioned duty ratio means a ratio of the totalcurrent feeding time to the predetermined control period, that is, thetime of feeding current per unit time (a current feeding ratio), or thetime of feeding power per unit time (a power feeding ratio).

In the embodiment, if the load switch 4 is turned on, the on-state timewidth of the output drive transistor 15 gradually increases, that is,the duty ratio of the current flowing in the electrical load graduallyincreases. A change rate of a duty ratio, namely, a change rate of apower feeding amount, for each of the electrical loads, which is shownas KR or KF in FIG. 3 (means of the symbols will be explained later) isstored in the memory 11b of the microcomputer 11. The change rate K of aduty ratio is a change amount of a duty ratio per unit time, equal tothe gradient K of a curve showing changes of a duty ratio expressed inthe coordinates of the abscissa of time and the ordinate of duty ratio,shown in FIG. 5.

Further, in the embodiment, even during the OFF state of the load switch4, the intermittent current is flowed in the electrical load 5 byintermittently driving the output drive stage transistor 15. Themicrocomputer 11 controls feeding of the intermittent current during aperiod To (the intermittent current feeding period) managed by using atimer T, and stopping the intermittent current during a period T1managed by using a timer TT. During the OFF state of the load switch 4,the duty ratio of the current flowing in the electrical load 5 is theminimum duty ratio, and a value of the minimum duty ratio for each ofthe electrical loads is stored in the memory 11b of the microcomputer11, expressed as Dmin in FIG. 3.

The CPU 11a of the microcomputer 11 executes various kinds of controlprocess in accordance with procedures shown by flow charts in FIGS. 6-9,described in programs stored in the memory 11b. The flow charts show theprocedures for one of the electrical loads, representatively, and aseries of the procedures are carried out with the predetermined period,for example, of 1 ms.

At step 301 of the flow chart in FIG. 6, a position of the key switch 2is checked. When the position of the key switch 2 is a position ofaccessories or engine stopping (a position other than ignition orstarter operating), the process goes to step 303, and "ST (stopping)" isset to a key position flag FLG. When the position of the key switch 2 isa position of starter operating (cranking), the process goes to step304, and "CR (cranking)" is set to the key position flag FLG. When theposition of the key switch 2 is a position of ignition (ON), the processgoes to step 302. At the step 302, an operational state of the engine isjudged based on the output from the engine revolution speed sensor 8c,and the process goes to step 305 and "ST (stopping)" is set to the keyposition flag FLG if the engine is stopping. On the other hand, if thedetected engine revolution speed is less than the predetermined speed,and it is determined that the engine is at an idling state, the processgoes to step 307, and "ID (idling)" is set to the key position flag FLG.If the detected engine revolution speed is equal to or more than thepredetermined speed, the process goes to step 306. At the step 306, itis judged whether the acceleration required by an operator is equal toor more than the predetermined speed, by estimating whether theoperation amount change of the accelerator conducted by the operator isequal to or more than the predetermined value (for example, 50 deg/sec),based on the output from the accelerator opening sensor 8a. If theacceleration required by an operator is equal to or more than thepredetermined speed, "AC (acceleration)" is set to the key position flagFLG at step 3061, otherwise "NM (normal)" is set to the key positionflag FLG at step 3062. Further, if the key position flag is ST(stopping) or CK (cranking), and it is judged that the engine is at thestopping state or the cranking state, the AC generator 3 is stopped bycutting off the field current of the AC generator 3 in order to reducethe consumption power, at step 308. On the other hand, if the keyposition flag is NM (normal), AC (acceleration) or ID (idling), becauseit is judged that the engine is rotating, the AC generator, 3 iscontrolled so as to keep the target standard voltage by thepreviously-mentioned control method, at step 309.

After the steps 308 and 309 for controlling the field current of the ACgenerator 3, the process goes to step 310 shown in FIG. 7. At the step310, the state of the load switch 4 is checked. If the state of the loadswitch 4 is an OFF state (directing a corresponding electrical load tostop), the process goes to step 311, and if an ON state (directing acorresponding electrical load to start), the process goes to step 381shown in FIG. 8, and if a transition state (indicating a statetransition from the OFF state to the ON state), the process goes to step317 shown in FIG. 7. The procedures following the step 310 is alsoexecuted for each of the electrical loads with a specified period.

At the step 311, it is judged whether the engine is at the stoppingstate or the starting state, that is, the key position flag FLG is ST(stopping) or CR (cranking), and further whether the timer T forcounting the time of feeding the intermittent current to the electricalload 5, indicates the predetermined time T0. If an intelligent typesemiconductor element having a current limitation function 16 is used asan element for driving an electrical load, namely, the output drivestage transistor, the current limitation function automaticallyoperates, and starting of the electrical load 5 is somewhat delayed,because the rush current at starting of the electrical load 5 largelyexceeds a limit of current flow for the semiconductor element 15. In theembodiment, in order to is prevent this problem, a small current (calledan idling current) is flowed in the electrical load 5 even during stopof the load 5. That is, at the step 311, if the key position flag FLG isnot ST and CK, and the engine is completely rotating, and the timer Tdoes not indicate T0, it indicates that the AC generator 3 generates thepower by rotation of the engine and power supply of the car issufficient. Therefore, the process goes to step 312, and the duty ratioof the intermittent current fed to the stopping electrical load 5 is setto the minimum duty ratio Dmin. As shown in FIG. 3, a value of Dmin isexpressed as a function of the key position flag FLG, that is, the valuechanges depending on the key position. At the step 312, the contents ofthe timer TT for counting the time of feeding the intermittent currentare also initialized to 0. At the step 311 also, if the key positionflag FLG is ST or CK, and the engine is not completely rotating, and thetimer T indicates To, it indicates that the power is not fed to the ACgenerator 3. Therefore, surplus power consumption is avoided by setting0 to the duty ratio of the intermittent current in order to stop feedingof the intermittent current.

After the duty ratio of the intermittent current is set at the steps 312and 313, the process goes to step 314. At the step 314, it is judgedwhether the time of feeding the intermittent current which is counted bythe timer T for measuring the intermittent current feeding time, is lessthan the time T0, and if the feeding time is less than the time T0, theprocess goes to step 315, and the contents of the timer T are increasedby 1. If the feeding time counted by the timer T for measuring theintermittent current feeding time, is equal to or more than the time T0,the process goes to step 316, and it is judged whether the time ofstopping the intermittent current which is counted by the timer TT formeasuring the intermittent current stopping time, is less than the timeT1. If the stopping time is less than the time T0, the process goes tostep 3161, and the contents of the timer TT are increased by 1. If thestopping time counted by the timer TT for measuring the intermittentcurrent stopping time, is equal to or more than the time T1, because theperiod for stopping the intermittent current has been finished, thecontents of the timer t for measuring the intermittent current feedingtime are reset to 0 in order to prepare the conditions for restarting ofthe intermittent current feeding. After the setting of the timers T andTT at the steps 315, 3161 and 3162, the process goes to step 333.

On the other hand, if it judged that the load switch 4 has indicated thestate transition, at the step 310, the process goes to step 317. At thestep 317, it is judged whether the state of the load switch 4 has beenswitched from the ON state to the OFF state. Further, if it is judgedthat the state transition from the ON state to the OFF state, namely,the transition state in feeding the power, has been indicated, theprocess goes to step 318, and if it is judged that the state transitionfrom the OFF state to the ON state, namely, the transition state forstopping the power, has been indicated, the process goes to step 320. Atthe step 318, a value of KR is set to the duty ratio increasing rate Kcorresponding to the electrical load 4, by looking up the control datatable (FIG. 3) stored in the memory 11b, prepared for adjusting of powerfeeding to the electrical loads, according to the various operationalconditions of the car. The value of KR is expressed as a function of thekey position flag FLG, and changes depending on the key position.Further, the process goes to step 319, and a timer TP for measuring thetime of a ON state of the load switch is initialized to 0. On the otherhand, at step 320, after the load switch is turned off, a value of Dminis set to the duty ratio of the intermittent current, as is the processat the step 312, so that the intermittent current immediately flows inthe electrical load 5. At step 321, the timer TT for measuring theintermittent current stopping time is reset to 0 so as to prepare theconditions for restarting of the intermittent current stopping. Afterthe setting of the timers TP and TT at the steps 319 and 321, theprocess goes to 333.

On the other hand, if it is judged that the load switch 4 is at the ONstate, at the step 310, and the process goes to step 322, it is judgedwhether the engine is at the stopping or starting state, that is, thekey position flag FLG is ST or CK, at the step 322, as is the process atthe step 311. If the key position flag FLG is ST or CK, and it is judgedthat the engine is not completely rotating, the process goes to step333, and if the key position flag FLG is not ST and CK, and it is judgedthat the engine is completely rotating, the process goes to step 323. Atthe step 323, it is checked whether the residual amount of fuel FUELremaining in a tank of the car, detected by the fuel amount sensor 8b,is more than the predetermined amount Flim. If the residual amount offuel FUEL is more than the predetermined amount Flim, the process goesto step 324, otherwise the process goes to step 325. At the step 324, itis further judged whether the key position flag FLG is AC, that is, theengine is at the acceleration state. If the engine is at theacceleration state, the process goes to the step 325, otherwise to step326. At the step 325, because the electrical load 5 is operating and theresidual amount of fuel is small, or the electrical load 5 is operatingand the engine is at the acceleration state, power supplies toelectrical loads of low functional importance are reduced in order toreduce the load of the engine. The reduction of power supplies to theelectrical loads of a low importance is carried out by setting anegative value KF prepared in the control data table (FIG. 3) stored inthe memory 11b, to a duty ratio changing rate for each of theseelectrical loads. The value of KF, as is KR mentioned above, changesdepending on the key position since it is expressed as a function of thekey position flag FLG, and has a negative value. At step 327, it ischecked whether the innovated duty ratio of the current is less than theminimum value Dmin, and if the innovated duty ratio is less than Dmin,the process goes to step 330 after the duty ratio is reset to Dmin atstep 328. On the other hand, at step 327, if it is judged that theinnovated duty ratio of the current is more than the minimum value Dmin,the process goes to step 329. If the engine is not at the accelerationstate at the step 324, and the process goes to step 326, a positivevalue KR prepared in the control data table (FIG. 3) stored in thememory 11b, is set to a duty ratio changing rate of the current fed tothe electrical load, as is the process at the step 318. Meanwhile, atthe step 326, the amount of remaining fuel is sufficient and the engineis not at the acceleration state. Therefore, since it is not necessaryto reduce the current fed to the electrical load in order to reduce theload of the engine, the positive value KR is set to the duty ratiochanging rate so as to increase a power supply to the electrical load 5.At the step 329, the present duty ratio of the current feeding isobtained by adding the product of the duty ratio changing rate K and theelapsing time TP from the turning-on of the load switch 4 to the presenttime, to the previous duty ratio. Further, at the step 330, it is judgedwhether the duty ratio obtained at the step 329 is equal to or more than100%, and if the duty ratio is equal to or more than 100%, the dutyratio is fixed to the upper limit 100%. Then, the process goes to step332. On the other hand, if the duty ratio is less than 100%, the processimmediately goes to the step 332. At the step 332, the counts of thetimer TP for measuring the time of a ON state of the load switch areincreased by 1 for preparing the control of the next time step.

After the setting of the timers T, TT and TP at the steps 315, 3161,3162 and 319, the process goes to step 333. At the step 333, it isjudged whether the key position flag FLG is CK, that is, the crankingstate, and if the engine is at the cranking state, the process goes tostep 334, otherwise to step 336. At the step 334, it is determinedwhether the present electrical load is to be stopped at the crankingstate, by referring to the control data table (FIG. 3) stored in thememory 11b. If the present electrical load is not to be stopped (forexample, a rear defogger), the process goes to the step 336, otherwiseto step 335. At the step 335, in order to stop the electrical load to bestopped at the cranking state, the duty ratio of the current fed to theelectrical load is set to 0, and the process goes to the step 336. Atthe step 336, the control signal is sent to the output front stagetransistor 14 so that the output front stage transistor 14 and theoutput drive transistor 15 feed the current corresponding to the dutyratio set at the steps 312, 313, 320, 328, 329 and 331, to theelectrical load.

FIG. 3 shows the preset data of the power duty ratio or the power dutyratio changing rate for a pair of headlights and a rear defogger asexamples of the electrical loads. As to the head light, if the engineoperational state flag FLG is other than CK, namely, the cranking state,values of KF, KR and Dmin are preset independently of the contents ofFLG. Because the value of Dmin is set to 5%, the current is alwaysintermittently fed to the pair of head lights even if the load switch ofthe pair of head lights is at the OFF state. Therefore, when the loadswitch of the pair of head lights is turned on, the pair of head lightsimmediately start lighting. Furthermore, feeding of the current to thepair of head lights is not cut even if FLG is CK, namely, the crankingstate. As to the rear defogger, the different values of KR and KR areprepared depending on the states of FLG indicating ID (idling) and NM(normal operation), or the states of FLG indicating ST (stopping) and AC(acceleration), respectively. Further, the minimum duty ratio Dmin isset to the duty ratio for the rear defogger because it is not requiredthat the rear defogger immediately start up when the load switch of therear defogger is turned on. Feeding of the current to the rear defoggeris cut if FLG is CK, namely, the cranking state, unlike the pair of headlights. The control data table shown in FIG. 3 is stored in the memory11b of the microcomputer 11, and the microcomputer 11 determines thepower duty ratio or the power duty ratio changing rate for each of theelectrical loads, by looking up the control data table stored in thememory 11b.

In the illustrated embodiment, at the state transition from the OFFstate to the ON state of the load switch, namely, the power feedingstart period, the duty ratio increasing rate KR is set at the step 318,and the amount of the power feeding to the electrical load graduallyincreases at a constant rate as shown by the lowest graph in FIG. 4, andin FIG. 5. Therefore, it does not occur that the power generated by theAC generator 3 rapidly increases. That is, it does not happen that theengine speed rapidly goes down, due to the rapid increase of the engineload at the power feeding start period. Furthermore, in the illustratedembodiment, even at the state other than the power feeding start period,if the load switch 4 is at the ON state, and the engine ordinarilyrotates, and sufficient fuel is left, and the engine is not accelerated,that is, it is sufficiently possible that the engine load is increased,the duty ratio increasing rate KR is applied to the duty ratio of theelectrical load at the step 326.

Further, in the embodiment, when it is not preferable to increase theengine load, for example, at the state of little residual fuel or engineacceleration, the duty ratio decreasing rate KF is applied to the dutyratio of the electrical load at the step 525. Thus, feeding of thecurrent to the electrical load gradually decreases at a constant rate,which reduces the engine load due to the power generation of the ACgenerator 3.

As mentioned above, in the embodiment, because the power feeding dutyratio or the power feeding duty ratio changing rate for each of theelectrical loads is changed corresponding to the state of the loadswitch 4 or the operational state of the engine, even if the power isfed to the electrical loads, the engine speed can be kept stable, whichimproves operational performance of the car.

Further, in the embodiment, at starting operations of the engine (thecranking state), the power is not fed to the rear defogger of lowfunctional importance fora definite time, even though the load switchfor the rear defogger is turned on. Therefore, a sufficient power issecured at starting operations of the engine, and the engine can beeasily and smoothly started.

Although the duty ratio changing rate is set to a constant value and theduty ratio linearly changes in the embodiment, changes of the duty ratioare not restricted to the linear change in the present invention, and itis possible to express the changes of the duty ratio with a curve, forexample, to set a group of time dependent differential coefficients tothe duty ratio changing rate.

Further, although one control unit 10 executes controls for feeding thepower to all the electrical loads, it is also available to control theelectrical loads by using a multiplex transmission system in a car (acar LAN system) in which a plurality of control units are connected witha multiplex transmission bus, as shown in FIG. 10.

An apparatus for driving electrical loads of a car shown in FIG. 10,comprises a CCU (Central Control Unit) 603 as a parent unit, LCUs (LocalControl Units) 607, 611 and 615 as child units provided at thevicinities of plural electrical loads distributed and arranged in thecar, multiplex transmission lines 605, 609 and 613 for electricallyconnecting among the control units, and a power line 2 for connectingbetween a battery 1 and the CCU 603, LCUs 607, 611 and 615.

The CCU 603 includes a microcomputer, signal processing circuits foradjusting the levels of outputs from sensors 8a, 8b and 8c to the levelsadequate to processing of the microcomputer, an input stage transistorfor inputting an output from a key switch 2 to the microcomputer, and atransmission IC (Integrated Circuit) for controlling transmissions amongthe LCUs 607, 611 and 615. The electrical loads 606, 610 and 614 areconnected to each of the LCUs 607, 611 and 625, respectively. Further,load switches 608 and 612 are connected to the LCUs 607 and 611,respectively. Each of the LCUs 607, 611 and 615 includes output stagetransistors driven by a driving signal, for feeding power to theelectrical load from the battery 1, a transmission LSI for sending thedriving signal to the output stage transistors and for controlling thetransmission between the LCU and the CCU 603. Further, each of the LCUs607 and 611 has an input stage transistor for inputting a switch-on/offsignal from the load switch 608 or 612.

When the CCU 603 sends data to one of the LCUS, the LCU which hasreceived the data, returns the data to the CCU 603. Therefore, both thedata sending signal and the data receiving signal are transmitted on themultiplex transmission line between the LCU and the CCU 603. The datatransmission between each of the LCUs and the CCU 603 is performed witha set of the data sending signal and the data receiving signal. To theCCU 603, a position signal of the key switch 2, signals output from thesensors, or switching state signals of the load switches output from theLCUs 607, 611 and 613, are input. The CCU 603 determines the duty ratioof the electrical load, of which the load switch is turned on, based onthese input signals, and drives the output stage transistors by sendingthe driving signal to the output stage transistors connected to the LCUvia the transmission LSI of the LCU, so as to feed the powercorresponding to the determined duty ratio, to the electrical load. Tothe electrical load connected to the transistors, the power is fed fromthe battery 1, corresponding to the ON/OFF state of the driventransistors.

As explained above, distributing and arranging a plurality of controlunits in a car can reduce the used amounts of a power line and signallines, in comparison with the centralized data processing method ofconnecting between a control unit, and plural electrical loads andplural load switches.

By using the present invention, at starting of the electrical loads,because the power fed to the electrical loads from the power source iscontrolled so as gradually to increase, it does not happen that the ACgenerator applies a rapid load increase on the engine, due to rapidincrease of the power generated by the AC generator, which stabilizesthe engine speed.

What is claimed is:
 1. A power supply system for a car, comprising:aplurality of control units coupled via transmission lines; a first groupof loads selected by a key switch, to which power is fed via a fuse; anda second group of loads connected to a power line without a fuse, inparallel, via a respective one of the plurality of control units forcontrolling each of said second group of said loads.
 2. A power supplysystem according to claim 1, further including a generator, current fedto field coils of said generator being controlled in response to controlstates of said first and second groups of said loads.
 3. A power supplysystem according to claim 1, further including an input circuit forinputting a position signal of said key switch.
 4. A power supply systemaccording to claim 1, wherein at least one of said first and secondgroups of said loads is controlled by a PWM method.